The objective of this project is to obtain methods to confidently identify each and every cell type in mammary gland cell cultures (epithelial, fibroblastic, adipose and myoepithelial). Only through precise knowledge of the type(s) of cells present in any cultured cell population under study, definite and conclusive biochemical, hormonal and cell biology experiments can be performed with them. Otherwise, measurements will reflect shifting values depending on the ratio of cell types present. To date, the criteria for identification of mammary gland cell types has been morphological and/or specific secretory product presence, both of which have limitations. Cell membrane markers (perhaps differentiation antigens) will be used to induce specific antibodies. With these antibodies and by the use of immunofluorescence, flow cytofluoremetry, cytotoxicity and radioimmunoassays, mammary cell cultures (both primary and established lines) will be identified as to their cell type of origin. In addition, these techniques will permit cell purifications of mixed cell populations by means of affinity chromatography or cell sorting devices. Cell antigen-markers used to immunize will come from injection of intact live cells, or cell membrane material released into the medium, or enzyme-solubilized components from the cell surface. In addition, human milk-fat globules (carrying apical epithelial cell membranes) will be the source of specific anti-human mammary epithelial cell antibodies to detect epithelial cells of human origin. These cell markers are the result of the phenotypic expression of the cell and their recognition will aid in the study of tissue and cell differentiation, and in tissue and organ specificity studies. The establishment of methods for separation and characterization of mammary gland cell markers could provide universal approaches to the identification of cell types of other tissues.